This invention relates to hydrotreating of hydrocarbon feedstocks and more particularly to catalytic treatment of hydrocarbon feedstocks to effect removal of nitrogen and sulfur, and to reduce Ramsbottom Carbon Residue (RCR). This invention is especially directed toward the preparation of a catalytic composition having excellent hydrotreating activity for the removal of nitrogen and reduction of Ramsbottom Carbon Residue in heavy hydrocarbon stocks. Examples of such heavy stocks are total crude oil, crude residue, atmospheric and vacuum gas oils, cycle oils and lube oils.
Crude petroleum oil, and heavy hydrocarbon fractions and/or distillates derived from crudes, contain components such as nitrogen, sulfur and metals. These impurities may exist in heteratomic compounds and are often present in relatively large quantities. Such impurities may poison or modify catalysts used in the upgrading of petroleum fractions in reforming or cracking steps. Nitrogen and sulfur are also objectionable because combustion of hydrocarbon fuels containing these impurities releases nitrogen and sulfur oxides. Such byproduct gases are noxious, corrosive and present a serious problem in the field of air pollution.
The removal and/or conversion of these impurities is effectively carried out by catalytic hydrotreating, where a feedstock containing sulfur and nitrogen is contacted with a supported catalyst in the presence of hydrogen. Hydrotreating conditions may include a wide range of temperatures, pressures and space velocities as determined by the design of commercial refineries.
Supported catalysts can be generally characterized as comprising metallic components, supported on a refractory inorganic oxide carrier of synthetic or natural origin and having a medium to high surface area (typically greater than 50 m.sup.2 /g) and a well-developed pore structure. Metallic components having hydrotreating activity may include the metals of Groups VIB and VIII of the Periodic Table. The "Periodic Table" as herein referred to appears in the 62nd Edition of the Handbook of Chemistry and Physics, CRC Press Inc., Boca Raton, Fl. (1981).
Group IVB metal components (for example, titanium) can be incorporated into the catalyst as a promoter to increase the activity of the catalyst. Phosphorous components are commonly incorporated into the catalyst to improve its activity by increasing its acidity; however, the prior art (U.S. Pat. No. 3,840,473) has taught that when the presence of phosphorous is greater than about 0.5% by weight in a titanium-containing catalyst, phosphorous is detrimental to the activity of the catalyst.
Numerous disclosures have been made directed to methods for preparing supported catalyst for hydrotreating. Catalytic metals may be applied to a formed or unformed carrier by several methods known in the art which include co-precipitation of the support with active metals and promoter (also known as the cogel method), mixing the active metals and promoter into a peptized substrate, and by various impregnation procedures on preformed substrates.
U.S. Pat. No. 3,401,125 discloses co-precipitation of the support with active metals including Group IVB to give an active hydrodenitrogenation catalyst. This method requires washing steps which are expensive, and metals, particularly the molybdenum, may be partially washed off the catalyst.
U.S. Pat. No. 3,897,365 discloses a process for preparing a hydrotreating catalyst comprising mixing molybdenum with an inorganic oxide gel consisting of at least 50 weight percent alumina, up to 50 weight percent silica, and up to a total 10 weight percent titania. The molybdenum oxide is from 5 to 15 weight percent. The catalyst is further impregnated with phosphorous, nickel and molybdenum.
The process for preparing a hydrotreating catalyst described in U.S. Pat. No. 3,897,365 differs from the method of our invention in that our invention involves mixing the Group VIII and Group VIB metals rather than impregnating these metals into the organic support.
U.S. Pat. No. 4,196,101 discloses a process for preparing a hydrodesulfurization catalyst comprising mixing alumina with water and a hydrolyzeable titanium compound under non-acidic conditions. Group VIII and Group VIB metals are subsequently impregnated into the inorganic support. The method described in U.S. Pat. No. 4,196,101 differs from the method of our invention in that our invention involves mixing the Group VIII and Group VIB metals rather than impregnating these metals into the organic support.
U.S. Pat. No. 4,465,790 discloses a hydrodenitrogenation catalyst comprising molybdenum and nickel on a catalyst support consisting of co-precipitated alumina and titania.
The method described in U.S. Pat. No. 4,465,790 differs from the method of our invention in that alumina and titania are not co-precipitated. Instead, the gelled Group IVB metal compound is mixed with a supporting oxide, the Group VIB and Group VIII metal components.
U.S. Pat. No. 4,444,655 discloses the use of a hydrotreating catalyst in a process for hydrotreating a heavy hydrocarbon oil containing asphaltenes. The hydrotreating catalyst utilizes inorganic oxides selected from Groups II, III and IV of the Periodic Table. The catalytic metal components are selected from metals belonging to Groups VB, VIB, VIII and IB of the Periodic Table.
The catalyst of the '655 patent has an average diameter of about 180 angstroms to about 500 angstroms, with total volume of such pores being larger than about 0.2 cc/g.